Info from the WKA website
362.8 WKA 125 SHIFTER Final 1 & Final 2:
DRIVER REQ: Age 18 and older. Road Race Class 2 Shifter license.
ENGINES: (1) Mass produced, single-cylinder, motorcycle engines of up to 125cc displacement, currently available production, approved by WKA: Honda CR Reed, Kawasaki KX Reed, Suzuki RM Reed, Yamaha YZ Reed, Gilera 125cc and TM Motocross will be allowed. (See Section 613 for specifications.) All engine specs must be unaltered OEM parts unless otherwise specified in this manual. All competitors must be prepared to produce verification documentation of proper dimensions and component data for the engine utilized for competition prior to the time of post tech inspection. (2) ICC engines with homologated pipe and 30 mm carburetor.
EXHAUST: Motorcycle engines – Any fixed WKA approved pipe (No adjustable pipes allowed) with silencer. ICC engines – stock homologated ICC pipe and silencer.
INTAKE SILENCER: ICC requires stock, homologated airbox. Motorcycle requires airbox (See 551.4.2) and/or air filter. Where specific track or ordinances requires the use of an airbox, this will be noted on entry form. Competitor is responsible to maintain compliance with any rules or ordinances regarding noise regulation.
∆FUEL: Open Fuel.
MINIMUM WEIGHTS: CIK bodywork – 410 lbs., WKA bodywork – 430 lbs.
TIRES: Open Compound, 5″ or 6″ Diameter Rims, Rear Tires 7.00″ Min. Width
OTHER: (1) CIK style bodywork allowed, either conforming to all dimensions listed in Section 200 (except the forward “C” dimension) or CIK approved bodywork that is readily available at least 90 days prior to the beginning of the racing season. Carbon fiber, Kevlar and metal are not legal construction materials for nose, side pods and steering fairing. (2) Radiator must be mounted on the right or left side of the driver between the tires. (3) All karts must use rear bumper rule 359.3.5. (4) Standing start procedure utilized. (5) Rear track width must be a minimum of 50″ and a maximum of 55 1/8″ on karts using CIK style bodywork. (6) Must use the 125 Sprint Shifter Seat rule described in Section 360.4.4. (7) No butterfly style steering wheels allowed. (8) WKA 125 Shifter runs both race days for a single championship. (9) WKA sprint bodywork allowed; bumper and nerf bar rules apply to these karts except that the minimum bodywork width as defined in 358.6.6 shall be 42″. Either CIK style side pods or Sprint Enduro side panels are allowed.